Electronic delay cartridge

ABSTRACT

An extremely compact electronic cartridge for delaying the delivery of a firing pulse to a squib which initiates a main charge. The delay provided by the circuit is maintained constant with temperature variations by using a thermistor in the circuit, and the original firing pulse is provided by a thermal battery.

United States Patent [72] Inventors William J. Brown King George;

Robert F. Butler, King George; Smith E. Hedden, Dahlgren; JanisJablovskis, King George, all of Va.

[56] References Cited UNITED STATES PATENTS 2,998,774 9/1961 Gibson102/702 P 3,099,962 8/1963 Smith 102/702 3,211,057 10/1965 White, Jr. etal. 102/702 3,225,695 12/1965 Kapp et al 102/702 3,343,493 9/1967 Auldset al.... 102/70.2 3,483,395 12/1969 Sauber 307/141 PrimaryExaminer-Benjamin A. Borchelt Assistant Examiner-Thomas H. WebbAttorneys Edgar J. Brower and Thomas 0. Watson, Jr.

ABSTRACT: An extremely compact electronic cartridge for delaying thedelivery of a firing pulse to a squib hich initiates a main charge. Thedelay provided by the circuit is maintained constant with temperaturevariations by using a thermistor in the circuit, and the original firingpulse is provided by a thermal battery.

PATENTEUUCT 19 l97l 3, 6 1 3 5 9 2 T if WILL MM 4. BROWN INVENTORSROBERT F. BUTLER SMITH E. HEDDON JAN/5 JAB/.OVSK/S ATTORNEY ELECTRONICDELAY CARTRIDGE GOVERN MENT INTEREST IN THE INVENTION The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States'of America for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION l. Field of the Invention This inventionrelates generally to devices for delaying the initiation of an explosivecharge and more particularly to an electronic delaying device havingsubstantially constant delay time with temperature change.

2. Description of the Prior Art In many applications, such as escapesystems, it is desirable to have a delay period between the timeinitiation action is started and the time the initiation of the mainexplosive occurs. For such applications, the prior art has generallyused pyrotechnic delay cartridges in which the original initiationaction ignited a percussion primer which in turn initiated a pyrotechnicdelay column. The pyrotechnic delay column was made of slowly burningexplosive which would delay the speed with which thedetonation wouldreach and initiate the main charge. A disadvantage of a pyrotechnicdelay cartridge is that the pyrotechnic mix in the delay column must bemixed and pressed under carefully controlled conditions in order tomaintain constancy of delay time. Regardless of the care taken inpreparing pyrotechnic delay cartridges delay time variations in excessof :25 percent are common, and delays over five seconds are verydifiicult to produce.

Electronic delay cartridges have also been proposed in the prior arthowever these have been bulky and the delay time would vary withtemperature changes. Also, the power sources used were normally ordinarybatteries whose power would decay with time even if not used.

SUMMARY OF THE INVENTION The disadvantages of the prior art have beenovercome by providing an extremely compact electronic delay cartridgeactivated by a thermal battery and having a thermistor in the delaycircuit to maintain the delay time constant with temperature variations.

It is an object of this invention to provide a delayed initiation deviceto electronically delay the initiation of a charge after starting theinitiation process.

It is another object of this invention to provide such a delayedinitiation device whose delay time is minimally affected by temperaturevariations.

It is still another object of this invention to provide such a delayedinitiation device which is extremely compact.

A further object of the'invention is to provide an electronic delayedinitiation device which can be activated by the application of heat.

It is another object of this invention to provide an electrdiiic delayedinitiation device which can be reliably activated long after it has beeninstalled in an explosive system.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows the basic construction ofan electronic delay cartridge according to applicants invention;

FIG. 2 shows applicants delay cartridge when the components are fittedinto a casing the size of a 38 caliber shell casing, and the details ofthe squib initiation system;

FIG. 3 shows the connection between the thermal battery and the printeddelay circuit according to applicants invention; and

FIG. 4 shows the electronic delay circuit of applicants device.

2 DESCRIPTION OF THE PREFERRED ahvitiomMENrs FIG. 1 shows the basicconstruction of the cic'ctr hic'aciay cartridge generally designated byreference numeral Il',c'o'rnprising a casing 12, having therein athermal battery I4 ;an' electronic delay circuit 15, a squib initiationsystem 16 and a main charge 18.

Thermal batteries are well known in the art and any, known thermalbattery could be used. Activation of the thermal battery can beaccomplished in a number of ways for example by means of a percussionprimer or by means of an electric match. Upon activation the thermalbattery provides a pulse of electricity to the delay circuit. The delaycircuit delays delivery of this pulse to the squib a predeten'riinedamount (if time, which is set by the circuit parameters. When'thepiils'e reaches the squib, the squib is heated and ignitesthe maincharge. I -j.

FIG. 2 shows in greater detail certain portions efa-delay cartridge suchas that shown in Fig. 1. A ca'sing t9 the a era 38 caliber cartridgecontains a thermal battery 20 andan electronic delay circuit 21. Theinitiation assembly 22 is of eonventional design and contains a bridgewire squib'26sur rounded by lead styphnate 25. Around the bridgewire-and lead styphnate is an ignition mixture 24. The ignition mixture24 is separated from main charge 28 by spacer I7 having-arr aperturetherethrou'gh to allow detonation of the main charge by the ignitionmixture. Upon delivery of the electric pulseby! the delay circuit tobridge wire 26 the lead styphria'te is ignited cuit board 35 to athermal battery 20. Leads 3 2 and Siextn'd through aligned apertures 37and a9, and $3 arid 38"in'the printed circuit board and the thermalbattery to connect the battery to the printed circuit. The p'riritedcircuittioard is then" placed adjacent the end of the thermal battery 20and the assembly is then inserted into casing into abutment withshoulder 23. Member 27, containing the igniter assembly and the bridgewire and ignition mix is then insert nto the cartridge, and leads fromthe bridge wire 'areplugg'edinto'the printed circuit board. Main charge'28 is than packed into member 27 and enclosure plate 29 is placed overth 'endiof the cartridge. The end of the cartridge 31 is then crimpedo'y'er an O-ring 30 to retain the entire assembly within casing.

FIG. 4 shows the novel delay circuit of the invention. Aconventionalthermal battery 20 is used to providepower to the circuit. A thermalbattery is one which is normally inert but upon application of heat isactivated to provide a pulsc r electricity to the circuit. Normallythis. is doiie by melting of an electrolyte which then flows into' thebattery to activate .it. Since the electrolyte is not normally thebattery thermal battery never deteriorates from setting inactive. Thismeaiis that it is reliable to provide power for initiation of anescapesystem or the like long after it has been installed, whereas aconventional battery could very well be discharged useless. Uponactivation of battery 20, capacitor 37 being charged through resistor36. Unijunction transistor 38 is normally reverse biased, but aftercapacitor 37 become suffi: ciently charged, the unijuncton transistorbecomes forward biased, thereby effectively shorting capacitor 37acrossre sistor 39 and the gate to cathode region of a siliconcontrolled rectifier 42. This pulse applied to thegate of the siliconcontrolled rectifier turns it on" thus applying power to the bridge wire26. v v To control the effect of temperature variations on the timedelay circuit, a thermistor I was placed in parallel with resister 40creating an equivalent resistance which varies with temperature.Variations of the resistance of the thermistor 4! with temperature willmaintain the time delay between activation of the thermal battery andthe supplying of power to bridge wire 26 essentially constant withtemperature. The resistance of resistor 40 has an effect on the voltageto which capacitor 37 must build to forward bias unijunction transistor38. By placing thermistor 41 in parallel with resistor 40, a temperaturevariable biasing resistance has been provided which compensates fortemperature induced variations in other circuit parameters to maintainsubstantially constant the time necessary for capacitor 37 to charge tothe level required to forward bias unijunction transistor 38.Experimentation has shown that the time delay period varies less than :3percent between the temperatures of -60 and +l60 F.

Thus it can be seen that an extremely compact electronic delay cartridgehas been produced which provides a delay time which is substantiallyconstant over a wide range of temperatures.

Obviously, many modifications are possible in view of the aboveteachings. For example, thyratron circuits could be employed instead ofsolid a circuitry. Also, this delay circuit could be used inenvironments other than explosive initiation. It would be useful anytimea temperature independent delay time is desired.

What is claimed is:

1. Means for delayed initiation of an explosive charge comprising:

an electronic delay circuit including means for maintaining time delayconstant with temperature variation;

a thermal battery actuable to provide power to said delay circuit; and

means connected to said thermal battery by said delay circuit toinitiate said explosive charge.

2. The device of claim 1 wherein said maintaining means comprises athermistor.

3. The device of claim 1 wherein said electronic delay circuitcomprises:

switch means;

means normally biasing said switch means open;

a capacitor which is charged by said thermal battery to overcome thebias on and close said switch means, and to discharge through saidswitch means to activate said initiation means;

said biasing means including the means for maintaining time delayconstant with temperature variation.

4. The device of claim 3 wherein said maintaining means comprises athermistor.

5. The device of claim 3 wherein said switch means comprises aunijunction transistor and said biasing means comprises resistorsconnected thereto, said maintaining means comprising a thermistor inparallel with one of said resistors.

6. The device of claim 5 further including a silicon controlledrectifier between said unijunction transistor and said initiating meansnormally preventing current flow from said unijunction transistor tosaid initiating means, said silicon controlled rectifier allowing suchcurrent flow in response to the discharge of said capacitor through saidunijunction transistor.

7. The device of claim 1, wherein said electronic delay circuitcomprises:

a first resistor and a capacitor connected in series across said thermalbattery;

a unijunction transistor having its emitter connected between saidresistor and capacitor;

a first base region of said unijunction transistor being connectedthrough a second resistor across said capacitor;

a silicon controlled rectifier having its gate connected to said firstbase region and its cathode in parallel with said second resistor, theanode of said silicon controlled recti fier being connected to saidinitiation means; and

a thermistor connecting said initiation means to a second base region ofsaid unijunction transistor, said second base region and thermistorbeing in parallel with said first resistor.

8. The device of claim 7 wherein said initiation means comprises afourth resistor.

9. An electronic delay circuit comprising:

a power source;

switch means;

means normally biasin said switch means open;

a capacitor which is c arged by sa|d power source to overcome the biason and close said switch means and to discharge through said switchmeans; and

said biasing means including thermistor means to maintain the timenecessary to overcome the bias on said switch means substantiallycontant with temperature variations.

10. The circuit of claim 9 wherein said switch comprises a unijunctiontransistor and said biasing means comprises resistors connected thereto,said thermistor maintaining means comprising a thermistor in parallelwith one of said resistors.

11. The circuit of claim 10 further including a silicon controlledrectifier between said unijunction transistor and said initiating meansnormally preventing current flow from said unijunction transistor tosaid initiation means, said silicon con trolled rectifier allowing suchcurrent flow in response to the discharge of said capacitor through saidunijunction transistor.

12. An electronic delay circuit comprising:

a power source;

a first resistor and a capacitor connected in series across said powersource;

a unijunction transistor having its emitter connected between saidresistor and capacitor;

a first base region of said unijunction transistor being connectedthrough a second resistor across said capacitor;

a silicon controlled rectifier having its gate connected to said firstbase region and its cathode in parallel with said second resistor;

an ultimate current delivery portion, said current delivery portionbeing connected to the anode of said silicon controlled rectifier; and

a thermistor connecting said current delivery portion to a second baseregion of said unijunction transistor, said second base region andthennistor being in parallel with said first resistor.

13. The circuit of claim 12 wherein said ultimate current deliveryportion comprises a fourth resistor.

1. Means for delayed initiation of an explosive charge comprising: anelectronic delay circuit including means for maintaining time delayconstant with temperature variation; a thermal battery actuable toprovide power to said delay circuit; and means connected to said thermalbattery by said delay circuit to initiate said explosive charge.
 2. Thedevice of claim 1 wherein said maintaining means comprises a thermistor.3. The device of claim 1 wherein said electronic delay circuitcomprises: switch means; means normally biasing said switch means open;a capacitor which is charged by said thermal battery to overcome thebias on and close said switch means, and to discharge through saidswitch means to activate said initiation means; said biasing meansincluding the means for maintaining time delay constant with temperaturevariation.
 4. The device of claim 3 wherein said maintaining meanscomprises a thermistor.
 5. The device of claim 3 wherein said switchmeans comprises a unijunction transistor and said biasing meanscomprises resistors connected thereto, said maintaining means comprisinga thermistor in parallel with one of said resistors.
 6. The device ofclaim 5 further including a silicon controlled rectifier between saidunijunction transistor and said initiating means normally preventingcurrent flow from said unijunction transistor to said initiating means,said silicon controlled rectifier allowing such current flow in responseto the discharge of said capacitor through said unijunction transistor.7. The device of claim 1, wherein said electronic delay circuitcomprises: a first resistor and a capacitor connected in series acrosssaid thermal battery; a unijunction transistor haVing its emitterconnected between said resistor and capacitor; a first base region ofsaid unijunction transistor being connected through a second resistoracross said capacitor; a silicon controlled rectifier having its gateconnected to said first base region and its cathode in parallel withsaid second resistor, the anode of said silicon controlled rectifierbeing connected to said initiation means; and a thermistor connectingsaid initiation means to a second base region of said unijunctiontransistor, said second base region and thermistor being in parallelwith said first resistor.
 8. The device of claim 7 wherein saidinitiation means comprises a fourth resistor.
 9. An electronic delaycircuit comprising: a power source; switch means; means normally biasingsaid switch means open; a capacitor which is charged by said powersource to overcome the bias on and close said switch means and todischarge through said switch means; and said biasing means includingthermistor means to maintain the time necessary to overcome the bias onsaid switch means substantially contant with temperature variations. 10.The circuit of claim 9 wherein said switch comprises a unijunctiontransistor and said biasing means comprises resistors connected thereto,said thermistor maintaining means comprising a thermistor in parallelwith one of said resistors.
 11. The circuit of claim 10 furtherincluding a silicon controlled rectifier between said unijunctiontransistor and said initiating means normally preventing current flowfrom said unijunction transistor to said initiation means, said siliconcontrolled rectifier allowing such current flow in response to thedischarge of said capacitor through said unijunction transistor.
 12. Anelectronic delay circuit comprising: a power source; a first resistorand a capacitor connected in series across said power source; aunijunction transistor having its emitter connected between saidresistor and capacitor; a first base region of said unijunctiontransistor being connected through a second resistor across saidcapacitor; a silicon controlled rectifier having its gate connected tosaid first base region and its cathode in parallel with said secondresistor; an ultimate current delivery portion, said current deliveryportion being connected to the anode of said silicon controlledrectifier; and a thermistor connecting said current delivery portion toa second base region of said unijunction transistor, said second baseregion and thermistor being in parallel with said first resistor. 13.The circuit of claim 12 wherein said ultimate current delivery portioncomprises a fourth resistor.